Joints for coaxial cable



y 1956 w. G. HILL JOINTS FOR COAXIAL CABLE 2 Sheets-Sheet Filed April 14 1951 may y 1, 1956 w. G. HILL 2,743,505

JOINTS FOR COAXIAL CABLE Filed April 14, 1951 2 Sheets-Sheet 2 [2 W1 V i z is VIIIII'IIIIIIIIIIIIIIIIIII .2 b

. INVENTOR. W/LL/AM C0RG /'//LL 4 TTOJCA/E United States Patent JOINTS FOR COAXIAL CABLE William George Hill, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 14, 1951, Serial No. 221,007 Claims priority, application Great Britain April 18, 1950 3 Claims. (Cl. 29-1555) This invention relates to coaxial telecommunication cables and in particular to joints in the coaxial cores of such cables.

Coaxial telecommunication cables are designed to operate at relatively high frequencies and at these frequencies the reflections introduced by the structural discontinuities at joints between adjacent lengths of coaxial core may result in impairment of the transmission properties of the cable. To obviate this it is customary to make the structural discontinuity at a joint as short as possible. In other words, the inner conductors of the two core lengths to be joined are connected together by means of a jointing ferrule slipped over and soldered to the two conductor ends and a short sleeve is slipped over the ends of the two outer conductors and soldered thereto. In order to provide access for welding or soldering of the abutting ends of the inner conductors it has been necessary heretofore to foreshorten the ends of both the outer conductors. As a result, when the ends of the inner conductors are in abutting relation there is a gap between the ends of the outer conductors and this gap is usually bridged by a short metal sleeve. There is therefore a small structural and therefore electrical discontinuity at such a joint since the sleeve over the outer conductor ends will be of slightly greater internal diameter than that of the outer conductor of the core.

A principal object of the invention is to provide improved methods of joining coaxial cable elements or lines, whereby the impedance characteristics are substantially uniform and electrical non-uniformities throughout the joint are reduced to an absolute minimum.

A feature of the invention relates to a method of joining the ends of two coaxial line sections by cutting back the outer conductor of one or both sections to leave the center conductor protruding for a substantial length to provide adequate space for welding or otherwise joining the abutting ends of the inner conductors. One of the cut-away ends of the outer conductor is then used as the splicing element for the cut-away end of the other outer conductor.

Another feature relates to a novel method of joining coaxial line sections whereby special splicing sections are avoided-resulting in substantial economy and improved impedance characteristics.

The nature of the invention will be understood from the following description of a joint made according to the invention and as illustrated in the drawing in which:

Figs. 1A and 1B illustrate one prior known method of forming a coaxial joint;

Fig. 1 shows in section a joint according to one embodiment of the invention;

Fig. 2 shows in section a tool used in the construction of the joint;

Fig. 3 shows in section another tool used in the construction of the joint;

Figs. 4A, 4B, 4C and 4D represent successive steps for lengths have been placed in position. The joints themselves can be made as short as is practically possible so as to minimize the discontinuity. There is, however, a disadvantage in making these short joints in that the soldered connection between the inner conductors and the two soldered connections between the outer sleeve of the joint and the ends of the two outer conductors are all rather close together so that the joint as a whole is somewhat rigid and liable to be damaged if subjected to bending. This is not of great importancewhen the joints are all made after the cable lengths have been placed in their final positions but occasions arise when it is desirable to make the joints between a number of lengths in the factory and then to transport the jointed cable to the locality where it is to be laid.

It is evident, for example, that joints in submarine cables must be made before the cable is placed in position. In these cases the joints should, so far as is possible have the same flexibility as the cable so that the complete length of cable including joints can be coiled on drums or in the tanks of a cable ship and passed around the cable ships paying out machinery.

A coaxial cable core of the type under consideration comprises a central or inner conductor surrounded by a tubular outer conductor maintained in coaxial relation with the inner conductor by insulating and separating means. A common form of insulating means consists of a regularly spaced sequence of slotted discs mounted on the inner conductor.

The outer conductor is usually constructed by the longitudinal folding of a metallic tape into tubular form, the two edges of the tape abutting along a seam parallel to the axis of the core.

In some cases the tape is provided with transverse corrugations to increase its flexibility.

So that the abutting edges of the tape shall not override they are provided with inter-engaging teeth or are otherwise specially shaped. It is also possible to provide a separate seaming strip consisting of a narrow H-shaped strip into which the edges of the outer conductors fit. The core is completed by an outer binding of steel tape which serves to keep the conductor tape edges abutting and also provides a magnetic screen. vention enables flexible joints to be made in all cores in which the outer conductor is formed by the longitudinal folding of a tape since it enables sleeves of any desired length to be used without introducing any appreciable impedance discontinuity.

Accordingly the present invention consists of a joint between two coaxial conductor cable cores comprising a relatively long outer sleeve connecting the outer conductors of the two cores that are jointed together said sleeve having substantially the same construction and dimensions as the said outer conductors.

It can be seen that the two soldering points and the point of junction of the two inner conductors may be sufficiently spaced apart as not to produce any undue rigidity in thejoint as a whole.

The invention further provides a method of manufacing a joint between two lengths of coaxial conductor cable core of the kind having an outer tubular conductor formed by folding a single tape longitudinally until the edges of said tape abut comprising the steps of removing from each of the core ends to be joined a dej sired length of outer conductor, slightly expanding for a short distance the two ends of a suitable length of The present inemptytuhe of. the same-construction, material and dimensions, as the outer conductors to form a,.sleeve with end sockets, opening up thelongitudinal seam in said sleeve, slipping said sleeve over the outer conductor ofronerof: the lengthsitosbe: joined; .joining thezinner: conductors, slipping said sleeve along to bridge: the" gapabetween? the: outer. conductors of the. two." lengths to. be joine.d,=.pressing. the edges of; said sleevetogether tore form itias; a tube:andtsoldering:or. welding the expanded endslof thertubular sleeveto the. endszofitheouten con: ductorsi of; the: two:- core: ends;

It. is: alsorpossiblerv to make: use-of part of the actual outer conductorrof one of: the: core: ends to. form: the sleeve without: detaching; the part frorn'the main length/ of! themuterconductors' as: will be explainedlater.

1 Normally-theserjoints Will-bcmatlerimthecable :factory'. and accordingly itzmajebe convenient to connectrthe; inner! conductors by buttnweldingxthe ends. The outer sleeve is. formed? oft a. length: of: tubular outer conductor; and maytconveniently. be: arpiece removed: from onerotithe: ends. at the time of! making; the joint; The length of the; sleeve; is; chosen according: to requirements and may be: as amuch'; as: twosfeetg. inrany case 2 it will. normally be considerably greater than thez'lengthrofs theisleeveiused'. whemflexibility is not important: The endsofr the tubu- 131". sleeve: are expanded slightly. for. a. short: distance,

sayrhalf: an inch,'.by=the:use of a specialtool soithat they.

wilhfit closely over: the: ends: of: the: cable outer' condoctors" to-form: a spigot and 1 socket joint.

The-tubular conductor isathen opened up" by: drawingor pushing through it atmandrel'of somewhat larger diameter; than' the: inner; diameter of the. tube. A" convenientttoolrfora therpurposedswa pull-through; as used for: cleaninggrifles in;whichthe"weight7 is: aihydraulic metal: body with: rounded; ends, the Weight being pulled thtOllghztl'lezfllbe on theiend of alength'of wire or string.

Thempenedlup sleeve is preferably'slipped .over' one of the cable ends before the joint in'thet inner'conductor is. madei After." the: inner conductor? jointzis1-rnade and the.-insulating structure z'put int place, .the 1 sleeve is slipped into: its' final position; and closed; so; that its edges: abut. The ends are then soldered or welded toithez ends-50ft thezcable; outer conductors. Thecore? joint: is finally completed with a bindingzofisteelztape.

Figs. 1A and-Fig: lBf show a". conventional methodlof forming ElizCOflXlHlTliHfil joint. The: outer'conductors of bothline sections arencut back with: respect-to: the inneri conductors so thatzaasuitable'welding tool, soldering tool, ortother'device' canbeinsertedto join-the abut ting ends of' the inner conductors together; Therefore, when the gapped outer-conductors are bridged" by 'a small metali sleeve asshown inFig. 1B there is a substantial nonuniformity of the inne-r diameter of the joined conductors:

In Fig. l' according to' the invention there are shown the two core ends I and'Z' which are-tob'e joined. The outer conductors 3 and 4 are cut at points 5and"6' while the=inner conductors extend to the centre of the joint where they are shown joined by means of'a ferrule 9 in the-normal'manner: As explained above, in some cases it may be preferable to make the joint between the inner conductors bybutt-Welding.

The. outer conductors 3and 4 are supported on insulating and separatingdiscs 10 and similar discs 11 are mounted on the exposedportion of the inner conductors 7 andS. It Will'be noticed that in the figure there are showntwo insulatingand'separating units each. built up of componentslland 13. These units are water. tight barriers. Component 12 is a hydraulic type washer such as is used'in a reciprocating water pump, and. is madeof'a resilient material such as soft rubber. Component 13f is an apertured disc. of a hard. insulating material whichispressed.into..the washer 12.. The. use of these-hydraulictype washers incable joints isdescribed in British Patent No. 678,236, filed on April 18, 1950 and. issued. on. December. 15,. 1952.

After the insulating discs have been arranged in position and the centre conductors joined the sleeve 14 connecting the outer conductors is applied. This sleeve consists of a length of outer conductor of exactly the same kind as that shown at 3 andi4ion the cable cores. A suitable length of tubularv outer. conductor. is selected and the ends are expanded by the use of'the press tool shown in Pig. 2,.in-which the piston -19-is pressed .into:the:.body-: 29 after the-endofrthe length of? tubular. conductor: has been inserted in the aperture 21- in the body 20. This results in the end. ofthe tube beingslightly expanded to form the socket 15' shown in Fig. 1.

When the; two. ends of the sleeve. 14i=have beenzexpanded to form the.sockets. 15 and 16 the length of tube is opened up along its longitudinal seam. This can conveniently be done by drawing the weight" of a pullthroughofsuitable diarneter through-the tube. In Fig-2 3 there is shown such a tool comprising a. weight 17 attached to a length of copper wire 18. Otherforms of mandrel would'zequaly- 'serve to-opemup the'sleeve; The opened: up sleeveis thenplaced in. position over the.

expanded. lengths. of inner conductors carrying the in sulatin-gzdiscssandipressedback 'into tubular: form-twithtthe edges adjoining; The.socketsilsiandzld are thenxsolderedi shown),

An.- alternative: method; of. making: a. which does-not involve :the use of;a:separate.-outer: sleeve is-illustrated-intl-" igs. 4A,;4'B, 4C and 4D. ASwShOWnZ-ilh Fig. 4A, .thetwo-core ends to berjoined are-broughtinto: position-with. aconsiderable overlap, such. as 9 to- 12!. inches or. more, and are firmlyheld. The outer. con-n duetor. ofoneoftthe ends,,.forv example the left-hand end, is thenzcutaway so. as,to leave onlyv about. /2? overlap,-

Withthe outer. conductor ofthe righthand. end,' as..in-..

dicatedl by, the. dot-.dashline running through Eigs..4Av and.4B. Theinner. conductor of the. lefthand section. willlnow, of-course, be projecting some 9. or. llinches. accordingtothe originaloverlap. The outer. conductor. of the righthandlsection is then spread openv bythe. use of a suitable tool; for a distance slightly greater; than the length of the projectingportion of the inner conductor ofthe left handsecticn, vas shown in Fig, 4C. The. endofthisspread-iopen section is expanded, as in: dicatedinJFig. 4D, toproduce' the socket'forthe spigot and'socket jointpreviously described. It will'be undere stood that this expansion can be efiectedbyusing the tool elements 19-and26 (Fig.- 2) so that when the-elementisforced into theopened-up endof the right hand line' section itforrnstlieexpanded socket.- The remainder ofth'e' right hand' sectiomis prevented from expanding and opening because itcloselyfits within the boreZl When-the expanded sock'et has been thus formed on' the end of the righti hand section the inner conductor" of that sectioniisxthen cut, asindicatediby the. dottedi line running through Figs. 4A, 4B and 4C, the cuttirrgnbeingl such that. the end: of? the: inner conductors oft both: sections abut'ragainstzeachzother; as-shown imFig; 41):. These:

abuttingcnds. of'..the;innen Conductors; are tllEIIs-jObIEd} as described above, after which: the-spIead-open:por+- tion of the outer conductor of.- the right hand section'is pressedebacle into position, andthe expandedsocket-endthereof .is-fitted over the non-expanded end of. the. outer; conductor of theleft handsection to whichit can. be soldered. As before, the joint is. completed with. a binding of steel tape.

It can be seen that the ratioof: thediameter ofQthe.

outer. conductor to that oi the inner conductors is substantially constant over the greater part of the. jointiso. thatimpedance discontinuity, is avoided, While the.sleeve can be made as long as is desired. Thejoint in thecentre. conductor is at some distance from the joints between flexible joint:

the sleeve and the outer conductors so that the flexibility is not seriously impaired.

It will be understood that this invention relates to the making of flexible joints in coaxial cable cores and that the invention can be used in conjunction with previously known methods for making water-tight barrier joints or substantialy reflection-free joints.

While the principles of the invention have been described above in connection with specific embodiments and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What I claim is:

1. The method of manufacturing a joint between two lengths of coaxial conductor cable core of the kind having an outer tubular conductor formed by folding a single tape longitudinally until the edges of said tape abut comprising the steps of removing from each of the core ends to be joined a desired length of outer conductor, slightly expanding for a short distance the two ends of a suitable length of empty tube of the same construction material and dimensions as the outer conductors to form a sleeve with end sockets, opening up the longitudinal seam in said sleeve, slipping said sleeve over the outer conductor of one of the lengths to be joined, joining the inner conductors, slipping said sleeve along to bridge the gap between the outer conductors of the two lengths to be joined, pressing the edges of said sleeve together to re-form it as a tube and soldering or welding the expanded ends of the tubular sleeve to the ends of the outer conductors of the two core ends.

2. The method of making a joint between two coaxial conductor cable cores of the kind having an outer tubular conductor formed by folding a single tape longitudinally until the edges of said tape abut comprising the steps of expanding the outer conductor for a short distance at one of the core ends sufliciently to fit over the other outer conductor, opening up the first mentioned outer conductor for a greater distance, cutting the inner conductor corresponding thereto and the outer conductor of the other outer end and bringing two ends of the two cores together so that the inner conductors abut in the middle of said opened up length of outer conductor and said opened up length overlaps the other outer conductor, joining the inner conductors together, pressing the edges of the opened up outer conductor together to re-form it as a tube and soldering or welding its expanded end to the other outer conductor.

3. The method of making a flexible electrical connecting joint between a longitudinally folded outer conductor of a coaxial cable and a longitudinally seamed malleable tubular member of similar outside and inside diameters to said conductor, comprising expanding for a short distance one end of said tubular member so that its inside diameter is approximately equal to the outside diameter of said outer conductor, opening up said tubular member along its longitudinal seam, slipping said tubular member over said outer conductor so that the ex panded end acts as a socket with respect to said outer conductor, and soldering or sealing the expanded end of the tubular member on said outer conductor.

References Cited in the file of this patent UNITED STATES PATENTS 311,522 Patterson Feb. 3, 1885 1,742,354 Hunter Jan. 7, 1930 1,911,775 Smith et a1. May 30, 1933 2,156,772 Seeley May 2, 1939 2,209,181 Wendel July 23, 1940 2,276,571 Grypma Mar. 17, 1942 2,402,451 Scott et a1. June 8, 1946 2,459,877 Gillis Jan. 25, 1949 2,499,853 Eckel et al Mar. 7, 1950 2,538,225 Alford Jan. 16, 1951 

